The Bayer Process for the recovery of alumina from bauxite ore is well known. The process entails the use of sodium hydroxide at temperatures ranging from about 120.degree. to about 250.degree. C. to extract the alumina. After the separation of the red muds, which are the insoluble residues remaining after the caustic reaction, the hydrated alumina is precipitated, after cooling, from the aluminate liquor, usually after seeding with seed crystals of trihydrate. The precipitated alumina trihydrate is then recovered, usually by filtration, and washed to remove moisture, i.e. residual liquor, which contains contaminants such as residual soda, which are detrimental to product quality.
It is well known to utilize various dewatering aids during the filtration process in order to assist in the removal of the moisture from the resultant filter cake so as to thereby minimize the cost of subsequent drying procedure.
A wide variety of dewatering aids have been employed for this purpose. U.S. Pat. No. 5,011,612 teaches the use of a C.sub.8 -C.sub.20 fatty acid or fatty acid precursor such as an ester or amide by adding it to the wash water or liquor slurry. U.S. Pat. No. 5167831 teaches the use of fatty acids of at least 12 carbon atoms in admixture with various non-ionic surfactants of HLB from 10-14. The use of amino functional silicones in conjunction with water and at least one surfactant is taught in U.S. Pat. No. 4,525,281.
A series of Japanese patents describe the use of 1) anionic surfactants such as C.sub.12 H.sub.25 C.sub.8 H.sub.4 So.sub.3 Na and sodium olefin sulfonates (JP 58 17, 816; CA 99:89899q), 2) sulfosuccinic anionic surfactants and, optionally, nonionic surfactants (JP 58 49, 416; CA 99:89900h), 3) anionic surfactants of alkyl phosphate salts (JP 58 49, 415; CA 99: 89901j), 4) nonionic surfactants such as C.sub.12 H.sub.25 O (C.sub.2 H.sub.4 O).sub.5 H (JP 58 17, 814; CA 99:107048t) and 5) alkyl sulfate anionic surfactants (JP 58 17, 815; CA 99:72605t) as dewatering aids in alumina trihydrate filtration. All of these references however, teach the use of the surfactant alone and only when added to the rinse water.
The use of dewatering aids in the filtration of mineral ores in general is also well known. U.S. Pat. No. 2,975,123 discloses the dewatering of various copper, iron and nickel sulfide or oxide ores using tertiary amino alkyl esters of fatty acids alone or in conjunction with a hydrocarbon oil while U.S. Pat. No. 4,039,466 teaches that various anionic surface active agents such as alkylbenzene sulfonates, sodium octylsulfosuccinates and polyethylene glycol types have been used to treat hydroextracted finely divided coal or silica but explains that these materials are not useful on finely pulverized ores. The patentee uses a nonionic compound having a polyoxyalkylene group and a cloud point of not more than 35.degree. C. in conjunction with an anionic compound having a hydrophobic polyoxyalkylene group in the molecule. Mineral oils may be added to the composition which is useful on metal sulfides, metal carbonates, metal oxides, metal silicates, bauxite, sand, cassiterite, fluorite and silica.
U.S. Pat. No. 4,097,390 relates to the use of 1) an ethoxylated secondary alcohol, 2) a dialkylsuccinic acid or salt and 3) a mono (ethoxylated alcohol) carboxylate ester of a sulfosuccinic acid or salt in the dewatering of filter cakes resulting from the flotation of ores such as chalcopyrite.
U.S. Pat. No. 4,207,186 relates to the use of 1) a hydrophobic alcohol of 8-18 carbon atoms and 2) a nonionic surfactant of the structure R--(O CH.sub.2 CH.sub.2).sub.x OH as a dewatering aid in the filtration of coal, iron ore, sulfides, oxides etc whereas U.S. Pat. No. 4,210,531 relies on the use of a combination of anionic surfactants such as dialkylsulfosuccinates, petroleum sulfonates, fatty acid soaps, alkyl ether sulfonates, alkyl sulfonates, alkyl phosphates etc and water-insoluble organic liquids such as aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aromatic alcohols, vegetable oils, animal oils etc to dewater copper and iron sulfides or oxides, salt minerals, coal refuse, fine coal etc. The only examples in this patent relate to coal treatment.
U.S. Pat. No. 4,231,868 teaches a process which dewaters coal and mineral concentrates using N-monosubstituted sulfosuccinamates e.g. copper and iron sulfides and oxides. Only iron ore is used in the examples.
In U.S. Pat. No. 4,410,431 there is disclosed the dewatering of coal, lead and taconite ores, glass sands etc with a blend of a tall oil fatty acid and an ethylene oxide adduct of a primary aliphatic alcohol. A commercial product designated as #2 comprising dioctylsulfosuccinate, sodium salt (85%) and #2 fuel oil (15%) is distinguished in the data graphically presented in the drawings.
A series of publications from Australia discuss dewatering of alumina trihydrate in considerable detail i.e. (a) D. J. Fox, M. S. Wainwright, S. J. Puttock, A. G. Fane, C. J. D. Fell, and R. G. Robbins, "The use of surfactant mixtures in the dewatering of alumina trihydrate." Light Metals (1987) 159-163; b) K. L. Tricklebank and M. S. Wainwright, "Characteristics of the dewatering of seed hydrate." Light Metals (1989(97-101; c) S. J. Puttock, A. G. Fane, C. J. D. Fell, R. G. Robins, and M. S. Wainwright, "Vacuum filtration and dewatering of alumina trihydrate--the role of cake porosity and interfacial phenomena." Int. J. Mineral Processing 17 (1986) 205-224; d) S. J. Puttock, M. S. Wainwright, J. W. McAllister, A. G. Fane, C. J. D. Fell, and R. G. Robins, "Characterization and dewatering of Australian alumina trihydrate." Int. J. Mineral Processing 16 (1986) 263-279; e) D. J. Fox, M. S. Wainwright, C. J. D. Fell, Y. C. Ho, A. G. Fane, and R. G. Robins, "The influence of Bayer liquor on the dewatering of a lumina trihydrate" Int. J. Mineral Processing 23 (1988) 85-92. These publications examine the use of a wide variety of surfactants for dewatering alumina trihydrate i.e. anionic surfactants (such as sodium lauryl sulphate and sodium dodecyl benzene sulphonate), cationic surfactants (such as cetyl trimethyl ammonium bromide and bis 2-hydroxyethyl cocoamine), and nonionic surfactants (such as ethoxylated alcohols and ethoxylated nonylphenols). Some combinations of surfactants were also used. In all cases, the surfactants were added to the wash water. Reference c also describes experiments in which an oil (olive oil or peanut oil) was added to the slurry before filtration and sodium dodecyl benzene sulphonate (SDBS) was added to the wash water. In these experiments, residual moistures were higher than obtained with the same dosage of SDBS alone.
All of the above references, while related to the subject matter of this invention, i.e. they all refer to the use of dewatering aids, are devoid of any teaching of the use of alkylsulfosuccinates in combination with oils in the dewatering of alumina trihydrate produced in the Bayer Process.